Virus discovered that makes you dumber

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Are you you? Modern science is asking this question with increasing persistence, whether through understanding of the mechanics of inherited characteristics or of the multiplicity of the brain. Probably the most area of research that most powerfully challenges our assumptions about self, however, is microbiology. A person’s gut “microbiome” is better at identifying them than their fingerprint, and you’ve probably heard that there are more bacterial cells in your body than human ones — more by quite a margin — but the sheer numbers are less affecting than how powerfully they can affect our behavior. Everything from indigestion to your level of energy can be dictated by the gut microbes without whom you would quickly die, and new evidence has implicated them in yet another aspect of life: intelligence.

In this case, we’re actually talking about a virus associated with microorganisms, an infectious agent called ACTV-1 that generally attacks algae. The researchers were doing research into the effect of viruses on the brain when they discovered ACTV-1 DNA in several participants’ throats. These participants displayed reliably lower scores on tests of spatial awareness and visual processing — but of course, perhaps people who are more likely to be hanging out near algae are also more likely to be dumb.

An algae cell infected with a similar virus to ATCV-1, shown in red.

To control for this, the researchers basically reran the experiment with mice, creating a control group not infected with ACTV-1; the infected mice were reliably less able to navigate mazes and perform other simple cognitive tasks. When they looked at gene expression in the infected vs. control mice, the researchers found that the virus was controlling expression of over a thousand genes. Viruses control gene expression in cells for a number of reasons — to end a threat to themselves, to end an alarm signal sent to the immune system, to kickstart replication of the virus’s own genome.

The passive, unemotional forces of evolution can give rise to some shockingly nuanced behaviors; we’ve all heard of the bird parasite that infects snails and forces them to be eaten by a bird. The issue is that the parasite only creates suicidal snails because it is a bird parasite, and the snail is just a means to get back into a bird. There’s no reason for a parasite to make its host dumber and thus more likely to die and take the parasite with it. This is almost certainly an emergent consequence of an impromptu hop from algal to mammalian cells.

What’s remarkable here is not precisely what the virus is doing, but how many of the participants were infected — 40 of the 92 participants! Remember that this study was not supposed to be looking for this particular virus, but found it almost half of the time.

This research begs the question: if there are thousands of species of microorganism in our bodies, and each of these comes with associated issues or pests like ACTV-1, then how much of our personalities might be dictated by the subtle interactions of many such intestinal hitchhikers? Maybe you’re a morning person — could that be a product of the variety of species in your belly, blood, and brain? And if so, how effectively could changing that species makeup change your personality? What if you are, unbeknownst to you, actually predisposed to be a bit perkier, a bit smarter, and a bit thinner than you are right now?

This study was only possible thanks to large-scale analysis of DNA from many, many species all at once — so-called meta-genomics. This allows scientists to do things like take a throat swab, or a soil sample, do large-scale analysis on all thousands of species’ worth of DNA it contains, and have a computer recombine it all into a sensible listing of species. The sort of meta-analysis can help farmers quickly learn what’s going wrong with a patch of soil, or an African aid worker whether a person’s cheek-swab has signs of any of a few thousand common diseases.

As we learn how to read and manipulate genetic information more and more powerfully, it’s not only our ourselves we will come to know more intimately. In better understanding the species that surround us and affect our lives, we will certainly achieve a better ability to control ourselves as well. But we should be ready to deal with the answers we get from such probing: if we find that our lives are dictated by a growing number of viral and bacterial actors, could public health become about controlling our internal diversity?